The present invention relates to an SiC single crystal including a relatively small number of dislocations and defects and a method for manufacturing the SiC single crystal, to an SiC wafer having an epitaxial film and a method for manufacturing the SiC wafer, and to an SiC electronic device, in which the SiC wafer is used.
Nowadays, an SiC semiconductor utilizing an SiC single crystal is expected to become a candidate material for next generation's power device substituting an Si semiconductor. However, according to study reports to date, it is thought that crystal imperfections in the SiC single crystal such as a micropipe defect, a screw dislocation, an edge dislocation, and a stacking fault are the causes of the leak current and the breakdown voltage lowering in the SiC semiconductor. Therefore, it is inevitable to reduce the leak current and suppress the breakdown voltage lowering in order to realize a high performance SiC power device. An SiC wafer with an epitaxial film is particularly used for the power devices. Therefore, an SiC wafer having an epitaxial film that does not include the crystal imperfections not only in the SiC single crystal wafer, on which the epitaxial film is located, but also in the epitaxial film is in high demand.
Incidentally, {1-100}, {11-20}, and {0001} are so-called plane indexes of crystal planes. Although the symbol “-” is conventionally placed on top of numeral in the plane indexes, the symbol is placed at the left side of the numeral in the present specification and drawings for the sake of convenience in document making. <0001>, <11-20>, and <1-100> represent directions in a crystal, and with respect to the directions as well, the symbol “-” is placed in the same manner as in the plane indexes.
An SiC single crystal includes a {0001} plane (c-plane) as a main plane orientation, and also includes a {1-100} plane (a-plane) and a {11-20} plane (a-plane), which are perpendicular to the {0001} plane. Conventionally, as a method to acquire an SiC single crystal, so-called c-plane growth method has been used. In the method, a seed crystal, in which a surface that is a {0001} plane (c-plane) of the hexagonal system or has an inclination smaller than 10 degrees from the {0001} plane is exposed as a seed crystal surface, is used, and an SiC single crystal is grown on the surface by sublimation-reprecipitation technique and so on.
However, the SiC single crystal grown on a c-plane, i.e., grown in a <0001> direction using a {0001} plane as a seed crystal surface includes micropipe defects at a density of 100 to 103 cm−2, screw dislocations at a density of 103 to 104 cm−2, and edge dislocations at a density of 104 to 105 cm−2 in the direction substantially parallel to the <0001> direction. In addition, if an SiC single crystal wafer is produced from the crystal grown on a c-plane and an epitaxial film is deposited on the substrate, the epitaxial film inherits the defects and dislocations that are exposed on the surface of the SiC single crystal wafer. Therefore, dislocations exist in the epitaxial film substantially at the same density as in the SiC single crystal wafer and affect undesirably on a variety of device characteristics.
To address the above problems, a method for acquiring a grown crystal 90 by growing an SiC single crystal on a seed crystal 9 having a seed crystal surface 95, which is an a-plane having an inclination of 60 to 120 degrees (preferably 90 degrees) from a {0001} plane, is disclosed in JP-A-5-262599, as shown in FIG. 6. It turned out that substantially neither micropipe defects nor screw dislocations are included in the crystal 90 grown on the a-plane.
However, the crystal 90 grown on the a-plane includes stacking faults 91 located on {0001} planes at a density as high as 102 to 104 cm−1 in the direction substantially parallel to the direction of the crystal growth. Moreover, the crystal 90 includes edge dislocations 92, which have Burger's vectors parallel or perpendicular to a <0001> direction and are substantially parallel to the direction of the crystal growth, at a high density. If an SiC single crystal wafer is produced from the crystal 90 grown on the a-plane and an epitaxial film is deposited on the substrate, the epitaxial film includes dislocations and stacking faults caused by the edge dislocations 92 and stacking faults 91 that are included at a high density in the crystal 90 grown on the a-plane. An SiC power device manufactured from an SiC wafer having the epitaxial film has a relatively high ON resistance and a relatively large leak current in the reverse direction. Therefore, the performance of the device can be undesirably affected.